A liquid crystal display device is a passive light emitting element, a display screen itself does not emit light, image display depends on a persistent backlight source provided by a backlight module in the liquid crystal display device, the light emitted from the backlight source is transmitted out of the liquid crystal screen through turn-on and turn-off of liquid crystal molecules, and the image display is finally realized. The backlight source and the liquid crystal display screen are combined together to form a liquid crystal display module. For example, in some liquid crystal display devices having a certain structure, a light source, an optical diaphragm and the like form a backlight source of a liquid crystal display; when the light emitted from the backlight source is irradiated onto a liquid crystal panel, the light is transmitted upwards through a lower polarizer, different liquid crystal panels would change the polarizing direction of the light according to their own mechanisms at this moment, and then the light is in contact with a color filter to produce colors and finally enters an upper polarizer; and after the polarizing direction is changed by the liquid crystal, one part of the light may be emitted out, the other part of the light is absorbed, and each pixel on the whole liquid crystal panel may decide respectively the intensity of the emergent light, so that an image is produced.